2.1.4 Enzymes

Question 1

What is meant by a biological catalyst?

Answer 1

• catalsyst = speed up reactions
• biological - reactions happen inside living organisms
  enzymes are proteins that speed up metabolic reactions

Question 2

Bords and mammals are entotherms. What does this mean and how does it enmsure enzymes function corrrectly?

Answer 2

• they maintain an optimum body temperature o, even if the external enviornmental temperature changes
• ensures enzymes work at maxinum rate + don’t denature

Question 3

Where can enzymes be found in household products?

Answer 3

biological washing powders
- remove biological molcules e.g. egg yolk
- can work at low temps
- save energy - good for environment

Question 4

What type of protein are enymes?

Answer 4

• globular
• have a specific 3d shape

Question 5

Give key features of globular proteins

Answer 5

• soluble in water
• have a specific shape
• have a tertiary structure
• have hydrophobic r groups on their surface
• have metabolic roles

Question 6

Give key features of enzymes

Answer 6

• globular proteins
• specific 3d shape
• soluble in water
• biological catalysts
• have an active site specific to one substrate
• their activity is effected by temperature, ph and concentration of substrate enzyme

Question 7

What is the difference between extracellular and intracellular enzymes?

Answer 7

extracellular = reactions occur outside the cell
ontracellular = reactions occur inside the cell

Question 8

Give examples of when extracellular proteins are used

Answer 8

• nutrients in polymer form are too large to enter cells via cell surface membrane - must be hydrolysed by enzymes into smaller components
• fungi break down molecules outside cell so they can be absorbed and used for growth
• enzymes in saliva + stomach which break down food

Question 9

Give examples of when intracellular proteins are used

Answer 9

Inside lysosomes to hydrolyse bacteria

Question 10

What factors affect rate of enzyme reactions?

Answer 10

• temperature
• concentration of reactants ( substrate + enzyme)
• ph
• presence of cofactors
• presence of inhibitors

Question 11

What is activation energy and how do enzymes affect this?

Answer 11

• the minimum energy required to start a chemical reaction
  -enzymes form enzyme-substrate complexes
• these speed up metabolic reactions witout the need for higher temperatures

Question 12

Name the two models of enzyme action

Answer 12

• lock and key
• induced fit

Question 13

What is a model?

Answer 13

• a simple representation of a process
• to help understand how the process works
• offen a visual representation

Question 14

Explain the key aspects of the lock and key model

Answer 14

• suggests the shape of the active site of the enzyme is complementory to shape of the substrate
• like a key is complimentary to its lock
• shape of active site doesn’t change

Question 15

Explain the key aspects of the induced fit model

Answer 15

• suggests the shape of the active site of the enzyme is not fully complementory to shape of the substrate
• as substrate collides with active site, active site changes shaoe
• causing active site to fit more closely with substrate
• puts strain on bonds, so they break more easily - lowering activation energy

Question 16

Why is the induced fit model more widely accepted by scientists?

Answer 16

• new technology + research from x ray crystallography
• more evidence that enzyme shape changed during reaction
• new evidence fits more closely with this model
• explains how enzymes lower activation energy

Question 17

How do higher and lower temperatures affect enzyme action?

Answer 17

Temperature Below Optimum
- low temperatures = less kinetic energy
- decreasing random collisions of substrate + active site per second
- less enzyme substrate complexes formed per second
- slower rate of reaction as less successful collisions
- enzyme not denatured

Temperature Higher But Still Below Optimum
- high temperatures = more kinetic energy
- increasing random collisions of substrate + active site per second
- more enzyme substrate complexes formed per second
- faster rate of reaction as more successful collisions
- enzyme not denatured

Question 18

What is temperature coefficient Q10 and how is it calculated?

Answer 18

A measure of how much the rate of reaction increases within a 10°C rise in temperature
Q10 = Rate at +10°C / Rate before

Question 19

What is an enzymes optimum temperature?

Answer 19

• the temperature at which the enzyme has the highest rate of activity
• 37°C in humans
• when enzyme denatures above its optimum temperature, Q10 no longer applies
• enzymes don’t denature under optimum temperature

Question 20

How do enzymes denature?

Answer 20

• as temperature increases enzymes have increase kinetic energy
• enyme vibrates more
• too much kinetic energy breaks hydrogen + ionic bonds
• causes 3D shape to change
• active site altered
• active site no longer complementary to shape of substrate
• substrate no longer binds
• enzyme-substrate complexes can no longer form

Question 21

Explain the basics of pH and how ions affect it

Answer 21

pH below 7 = acid = higher concentration of H+ ions
pH above 7 = alkali = higher concentration of OH+ ions

Question 22

How does pH affect enzyme action?

Answer 22

• charged ions attract to or repel from charges in protein structure
• charged ions interact with polar and charged R groups - changing ion concentration cahnges this interaction
• these could change the charge of the R-groups of the active site (could affect binding of substrate)
• tertiary structre (3D shape) of active site changes
• substrate binds less efficiently - less enzyme-substrate complexes form - enzyme denatured
• eventually, active site no longer complimentory to substrate, so can no longer bind

Question 23

What is renaturation?

Answer 23

Small changes in pH away from optimum pH, followed by return to optimum pH causes active site to return to complimentory shape

Question 24

What is initial reaction rate and why is it also the highest reaction rate?

Answer 24

• the maximum possible reaction rate for an enzyme under a particular experimental solution
• when first mixed together reaction rate is highest
• as reation proceeds, product moleciules are formed + substrate molecules are used up and decrease in concentration
• frequency of collisions decreases as reaction proceeds

Question 25

What is a limiting factor?

Answer 25

The factpr that will determine the rate of reaction when at sub-optimal level. Prevents the rate from increasing and causes a plateau.

Question 26

Give examples of limiting factors and how cells use them

Answer 26

• temperature (if too cold)
• concentration of substrate
• concentration of enzyme
• cells regulate concentration of enzyme + substrate to control metabolism

Question 27

How will an increasing substrate concentration affect the rate of an enzyme-controlled reaction?

Answer 27

• to begin, substrate is limiting factor, so rate will increase
• after all active sites are occupied of enzyme, substrate concentration wil not afect rate as enzyme is limiting factor

Question 28

What is an inhibitor and what are the two types?

Answer 28

A substance that slows down the rate of an enzyme catalysed reaction by affecting the enzyme in some way
- competitive + non-competitive

Question 29

How do competitive inhibitors work?

Answer 29

• have a similar shape to substrate
• fit into active site to block substrate from binding
• fewer active sites + fewer enzyme-substrate complexes made
• reduces rate of reaction
• most can leave active site (non permanent)

Question 30

How do non-competitive inhibitors work?

Answer 30

• bind to allosteric site (away from active site)
• changes shape of tertiary structure + 3D shape of enzyme
• active site shape altered - substrate can no longer fit
• fewer active sites + fewer enzyme-substrate complexes made
• reduces rate of reaction
• can be permanent

Question 31

How can the effect of inhibition by competitive inhibitors be increased?

Answer 31

Increase in concentration compared to substrate molecules - greater chance of inhibitors colliding with active site = greater chance of inhibition

Question 32

How could you find out if a competitve or non-competitive inhjibitor was used on a graph showing initial rate of reaction compared to substrate concentration?

Answer 32

Competitive Inhibitor
- increasing the concentration of the substrate will reduce the inhibition effec
- if as the increasing substrate concentration increases, the rate of reaction increases and eventually reaches a maximum plateau, it suggests competitive inhibition
- reason for plateau = at higher substrate concentrations, most enzyme active sites are occupied by the substrate, reducing the impact of the inhibitor

Non-competitive Inhibitor
-increasing the concentration of the substrate will not fully overcome the inhibition effect
- visible decrease in the maximum rate of reaction, but substrate concentration remains unchanged
- inhibitor binds to a different site on the enzyme, affecting its activity without competing with substrate

Question 33

What is a metabolic pathway?

Answer 33

Sequences of chemical reactions each controlled by a specific enzyme

Question 34

What is a cofactor and name two types, as well as another molecule that enzymes sometimes need to function

Answer 34

Any substance that must be present for an enzyme-controlled reaction to take place at the appropriate rate
- coenzymes
- inorganic ions

• prosthetic groups (not classed as a cofactor, as permanently bound to enzyme)

Question 35

Give key aspects of coenzymes

Answer 35

• often made from vitamins
• smalll, organic, non-protein
• bind loosley with the active site before or after the substrate does
• can be recycled to take part in the reaction again
• can take chemical groups from one enzyme to another, forming a link between them

Question 36

Give key aspects of inorganic ions

Answer 36

• can bind with the enzyme or substrate
• binding of ions to the enzyme can make enzyme-substrate complexes form easier
• can affect charge disttribution + change shape of active site

Question 37

Give key aspects of prosthetic groups

Answer 37

• permanent part of enzyme
• contribute to the final 3D shape
• bound tightly to enzyme

Question 38

What is a precursor activation?

Answer 38

• many enzymes made in an inactive form (inactive precursor enzymes)
• important for enzymes that could damage cells
• often need to undergo changes in shape to become activated
• changes in shape can occur via addition of cofactor or action of another enzyme
• can also activate due to pH or temperature changes

Question 39

Explain how blood clotting occurs using enzyme activation

Answer 39

• platelets move towards site of tissue damage, releasing clotting factors (thromboplastin)
• thromboplastin is an enzyme dependant on cofactor Ca2+ ions
• once activated, catalyses conversion of prothrombin into enzyme thrombin (cleaves bonds to alter tertiary structure)
• thrombin (protease) catalyses conversion of solube fibrinogen into insolule fibrin fibres - clots blood

Question 40

What is an independent, dependent and control variable?

Answer 40

Independant = variable that is changed - x axis
Dependant = variable that is measured - y axis
Control = variable that is kept the same otherwse results are invalid

Question 41

What is an control, negative control , and positive control group

Answer 41

Control group = a standard comparison for checking the results of an experiment
Negative control group = a control group that is not exposed to the experimental treatment or any other treatment expected to have an effect
Positive control group = a control group that is not exposed to the experimental treatment, but is exposed to another treatment known to have the expected effect

Question 42

What is meant by accuracy?

Answer 42

A measure of closeness of agreement between an individual test result and the true value

Question 43

Why are experiments repeated?

Answer 43

• to identift and remove anomalous results - to reduce the impact of anomalies
• to measure and increase repeatability
• to calculate a mean, standard deviation and a statistical test
• improves confidence in the results